Serpentine Alternator - 2 or 3 wire

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Guys,

Simple question.

Is the Serpentine Alternator - 2 or 3 wire ?

I have converted my wedge to serpentine and with a new alternator
but my old set-up was 2 wire and after starting the car the battery voltage
is < 12 volts .. so perhaps something is wrong.

[dnb]

2 wires are used. The 3rd can be used for an RPM signal, but is not connected to anything assuming my car is typical.

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Excellent - Thanks.